The present invention relates to capacitors and tantalum powders of capacitor grade, used in production of miniature, high-specific-capacitance, low-leakage, solid state electrolytic and wet electrolytic capacitors with anode pellets or slabs made of sintered valve metal powders, e.g., tantalum,.
It is known in the art that phosphorous doping retards sinter closure of tantalum powders used in anode production to preserve a high capacitance of the tantalum powder. However, increasing levels of phosphorous doping also produce unacceptable increases in D.C. leadage, particularly in anodes formed (oxidized) at lower temperatures, e.g. 60.degree. c.
It is a principal object of the present invention to provide an improved capacitor grade tantalum powder affording practical high capacitance at low leadage and to produce anodes therefrom, formable at over 40.degree. C. and throughout the range 40.degree.-90.degree. C.
That is, the anode is to be formable at any temperature in such range consistent with high capacitance and low leakage (whereas prior art items have unacceptably high leakage at the lower portion of such range). The terms "form", "forming" "formable" and the like refer to the well known wet process of anodic oxidation to establish a tantalum oxide surface film as a capacitor dielectric element at the surface of the tantalum powder particles.